1. Field of the Invention
The invention relates to histologic tissue processing and more specifically to composite tissue processing and embedding structures.
2. Description of the Prior Art
The two-part structure taught by U.S. Pat. No. 2,996,762 to James B. McCormick includes an embedding box which is comprised of a boat receptacle and a paraffin housing structure which is adapted to be received by the microtome device. The housing structure is loosely placed or seated on the boat receptacle after the tissue specimen has been positioned in the boat receptacle and the composite structure is filled with liquid paraffin. The boat receptacle is removed from the housing structure after the paraffin has hardened and may be reused or discarded while the housing structure in which the paraffin tissue block remains may be placed in the microtome and have certain sections cut from the same after which the remainder of the paraffin block and the housing structure is catalogued and filed for future reference. The housing structure is provided with internal projections which secure the molded block to the housing and with an external flange which is required for the same to be placed in a microtome device in alignment with the microtome cutting blade. The internal projections interfere with positioning of the specimen and thus it has been the practice to position the tissue specimen in the boat receptacle before seating the housing structure on the boat receptacle.
In order to prepare a tissue specimen to be placed into the embedding structure of McCormick, the tissue specimen must first be exposed to the usual processing liquids such as alcohol, xylene, liquid paraffin, and the like, and which under conventional practice requires a separate type of receptacle for holding the tissue. That is, unlike the two-part structure of the present invention, the McCormick housing and boat elements have no utility as a processing receptacle, and consequently a separate processing structure, such as disclosed in U.S. Pat. No. 3,128,902, is required. The use of separate processing and embedding receptacles necessitates a removal of the tissue specimen from the processing receptacle after processing and a transfer of the tissue to the embedding receptacle.
The above practice was greatly improved by the introduction of the three-part processing and embedding receptacle taught by U.S. Pat. No. 3,456,300. This structure eliminated the need to remove the tissue specimen from the processing receptacle and transfer it to a separate embedding receptacle. However, it has been found that this structure takes up a great deal of space during processing and thus substantially reduces the number of tissue specimens which can be processed in a given cycle. The structure of U.S. Pat. No. 3,456,300 is also more expensive to manufacture and more complicated to use than the present invention.
U.S. Pat. No. Re. 28,165 discloses a three-part processing and embedding device. The device comprises an open-topped, box-like processing pan having a perforate bottom wall, a perforate cover member and an open-topped, box-like base embedding pan. For processing, the tissue specimen is placed in the processing pan and the cover is placed over it to make an integral, perforate processing unit. After processing, the cover is removed and the tissue specimen is lifted out of the processing pan and transferred to the embedding pan. The processing pan is then placed in coupled relation over the embedding pan to form an embedding unit. This patented device teaches the use of the perforate bottom wall of the processing pan as the means for trapping the hardened paraffin body. However, the principal drawbacks of this device are that it requires three parts and its use requires that the specimen be transferred from one pan to another, thereby risking the loss of identity of the specimen and damage to the specimen. No teaching in this patent suggests the design of a two-part receptacle useful for both processing and embedding and which does not require the specimen to be lifted and transferred from one pan to another.
Another three-part structure is taught by U.S. Pat. No. 3,411,185. A further type of three-part receptacle having a telescoping arrangement is taught by allowed copending application Ser. No. 487,463, filed July 11, 1974, and entitled "Compact Telescoping Tissue Processing, Embedding Microtome Holder and Storage Receptacle". This latter type of receptacle uses substantially less space than prior receptacles but does require three parts.
U.S. Pat. No. 1,867,447 to F. J. Dunn teaches a two-part display box made from light wood or fibrous material and adapted for storage and display of articles such as cigars and candy. The box comprises two open-ended, box-like members which join together in a first configuration to form a closed, imperforate box and in a second configuration, with the cover supporting the base, to form a display box for displaying the articles to be vended. This patent does not suggest the use of a similarly constructed box in the tissue processing and embedding art. The Dunn box does not lend itself to the processing and embedding of tissue speciments for a number of reasons. First, the display box would not allow embedding of tissue because it has straight sidewalls. When paraffin hardens, an angled wall is required to allow removal of the hardened paraffin body. Secondly, for processing tissue, a perforated cover is required to allow fluid penetration into the unit and to allow drainage after each processing fluid is introduced into the unit. Third, the bottom surface of the embedding unit must be thin and have heat transfer characteristics which will allow rapid cooling of the tissue when embedding with molten paraffin. Fourth, the materials used in the construction of tissue processing and embedding units must be selected with great care so as to be inert to the harsh fixatives and solvents used in processing. The material must also be capable of withstanding the heat used in melting of the paraffin. The material must be non-absorbent so that it will not absorb the various processing fluids and will not absorb the molten paraffin. An absorbent material would swell during the process and make it impossible for the dimensions of the unit to be retained during the process for proper securement. Furthermore, the material must be sufficiently rigid and sturdy to withstand the pressure from the opposed jaws of a microtome clamp. It is believed, therefore, that the Dunn display box and similar boxs are wholly inadequate to teach, suggest, or make obvious the use of a two-part receptacle for the processing and embedding of histologic tissue specimens.
It can thus be seen that the prior art teaches a two-part device for embedding and subsequent operations and a number of three-part devices which are useful for processing, embedding, slicing and storage. However, with the increasing number of histologic specimens being processed in medical centers throughout the world, there is an acute need for a simple, inexpensive, two-part structure which is useful for all of the operations, i.e., processing, embedding, slicing and storage. Such a structure has not heretofore been available.